In cognitive networks, cognitive (unlicensed) users need to continuously monitor spectrum to detect the presence of primary (licensed) users. In this paper, we illustrate the benefits of cooperation in cognitive radio. We show that by allowing the cognitive radios operating in the same band to cooperate we can reduce the detection time and thus increasing their agility. We first consider the case of two cognitive users and show how the inherent asymmetry in the network can be exploited to increase the probability of detection. We then extend our work to multiple cognitive user networks. We also propose a practical algorithm which allows cooperation in random networks